Thursday, May 5, 2011

Air Gap along the top

Early diagram trying
twin mirrors at foot
5 May '11: I Climbed the ladder to re-fix the aluminium cover to the outlet pipes, but while up there realised that there is an airgap at the top the thickness of a finger all the way across the top of both boxes. 
   In the section the airgap is behind the upper mirror, so perhaps rain is able to run down the back too.... Rain? What rain? we haven't seen any since March!

When building the boxes I had the idea that ventilation of the boxes would help, but as I have used them for over a year, it has become apparent that for the greatest part of the time, they are better being airtight. They never overheat, the temperature gets to a maximum of mid forties, and that is quite safe - as long as the black chillers work, they are drawing heat away and this never exceeds low twenties, because the heat is being dumped.
  I am not sure what the sunbox air temp would be if I turned the pump off on a very hot day. If there is a temporary shut down due to a faulty pump, energy meter or thermostat, it could go up to 50º but I have vents top and bottom to release the heat.
  I will try to source some compressible foam to put up there, and then check the resulting temperatures. A more permanent fix would be some thin gauge aluminium to put across the gap. 
   This section through the boxes shows the upper mirrors, and their 60º angle. Ignore the lower mirrors, I decided after the upper ones worked well to make the foot mirror simpler and single. The dotted blue lines in the diagram illustrate the solar midday angles for summer, equinox and winter.

2 comments:

  1. if you draw the reflection angles of the rays on the top mirror you see that the mirrors do not reflect light towards the panel..

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  2. I couldnt think of an easy way of adjusting it that i could manage that high off the ground. also, it was my first major exercise using the ladders since the scaffolding was taken down. I am now more confident up the ladder and may get up there to add a stiff hinging arrangement, that only needs adjusting every 2-3 months - or can be some from the bedroom window.

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